The Aon Center is a structural tube, with major columns placed on the exterior perimeter of the tower for increased stiffness. This gives the tower its strong vertical architectural lines.

The Aon Center has 83 floors and was originally called the Standard Oil Building, earning it the nickname "Big Stan". It was the tallest building in Chicago for a brief time before the completion of the Sears Tower. Despite its lower floor count, the Aon Center's roof is actually 9ft higher than the more famous 100 story John Hancock Center.

Looking down on the roof top. For many years the Aon Center was the tallest building in the world without a major communication mast, architectural spire, or public observation deck. In the summer of 2009 a roughly 50ft tall communications antenna was installed on the roof.

The sunken plaza along the Randolph Street entrance.

The plaza waterfalls along Randolph Street.

The covered entrances on the backside of the property.

The tower model appears quite simple from the outside. However the inside requires a more complicated structure to hold it all together. Each face of the builing is actually comprised of two halves with the studs pointed away from the other. The two halves are held together by bar elements. The four faces are then connected at the corners using hinge bricks.

A view showing the top most module removed from the tower. The modules are stacked and held together at their interfaces via eight technic pins. The model is comprised of four of these modules.

Great structure!! As usual you've managed to replicate another famous skyscraper with pinpoint accuracy. Having been to Chicago many times, I know exactly what this building looks like and you did great!

Quoting Sean Kenney
I'm surprised you didn't use the same technique as your WTC, though, since they have such similar façades. Any thought to doing the WTC with this technique? ;)

Sean, I originally thought about using this technique for my WTC model, but the cost and piece availability at that time wasn't in my favor. It wouldn't work so well for me now because I would need to greatly increase the scale of my WTC to simulate a reasonable number of columns. When viewed from a distance, the Aon Center has a stronger vertical column presence than the WTC because the columns, while fewer in number, are each much larger in size. The stark contrast of using white tile grilles against the black windows would have disrupted this strong vertical continuity.

I always thought this would be a fun but easy Lego build. Obviously it was not easy! You did a great job. And as I have visited my friend who works in the plaza many times, I can tell you it's very accurate. Well done!

The AON Center. Perhaps my favorite skyscraper in Chicago. You captured it. Quite wonderfully. Randolph street and the small plaza at the ground floor are perfect remakes of the real thing. Overall, you did a fantastic job on this model. The structural concepts are quite astounding. You are probably the best skyscraper builder here, and the inspiration for my WIP Skyscraper.
Congrats on a job well done, Spencer.
~Tom